The present invention relates to a photometering apparatus for use in a chemical analyzer, and more particularly to a photmetering apparatus of a direct measuring type in which a colorimetric measurement of a test liquid is effected, while the test liquid is still contained in a reaction vessel.
There have been proposed various kinds of such a direct measuring type photometering apparatus. For instance, in a Japanese Patent Application Laid-open Publication No. 113,383/76, there is disclosed a photometering apparatus in which a reaction vessel made of transparent material is arranged in a thermostat of an air-bath type and an absorption of a test liquid contained in the reaction vessel is measured by transmitting a measuring light beam through side walls of the reaction vessel. However, the thermostat of air-bath type cannot keep a desired temperature in a prompt and precise manner as compared with a liquid type thermostat and thus, a time required for effecting the photometry is liable to be long and further a high measuring accuracy could hardly be obtained. In order to overcome such a drawback one may consider to use the liquid type thermostat instead of the air-bath type thermostat. However, in such a case the photometry has to be performed through a liquid in the thermostat and thus, the high accuracy of measurement could not be attained due to absorption in the temperature conrolled liquid in the thermostat.
Further, in the known apparatus, since the measuring light beam is passed through the side walls of reaction vessel in a radial direction, dimension of the reaction vessel should be made accurate in order to obtain an accurate length of an optical path and therefore, a cost for manufacturing the reaction vessel becomes high. Moreover, in case of a multi-channel analyzer, the reaction vessels in adjacent channels should be separated by a relatively large distance in order to eliminate mutual interference, and this results in that the apparatus is liable to be large in size. Moreover, an optical system of a photometering unit is liable to be complicated and a loss of light becomes large to decrease the measurement precision.
In a U.S. Pat. No. 3,999,862, there is described a photometering apparatus of quasi-direct type. In this apparatus, a reaction vessel and a photometeric cell are formed integrally into a single vessel and a test liquid is transferred from the reaction vessel to the photometric cell by means of centrifugal force. However, this apparatus could not be applied to the multi-channel analyzer and has a low processing ability, because the test liquids could not be treated continuously. Further, since use is made of the centrifugal force, a driving mechanism becomes complicated and expensive. Moreover, the photometry has to be effected during the rotation, a data process becomes extremely cumbersome. Since a temperature regulating liquid is transferred to the photometric cell by means of the centrifugal force and thus, the photometric cell is exposed, while the rotor is not rotated, the temperature of the test liquid could not be regulated well and a measuring error is introduced.
In addition to the direct measuring type explained above, a flow cell type photmetering apparatus has been proposed. However, in the flow cell type apparatus, since the test liquid must be transferred from the reaction vessel to a flow cell by sucking force, a substantial amount of the test liquid is required. In recent, a quite large number of test items have to be effected for respective samples and to this end an amount of the test liquid should be corresponding small. The flow cell type apparatus does not satisfy such a requirement. Further, since the flow cell has to be used for successive test liquids, there occurs a problem of contamination to decrease the measuring precision. In order to avoid the contamination, there must be provided a complicated mechanism for washing the flow cell.